I found a clear glass decanter with a glass stopper at my grandfather's house engraved with the words "BONNIE & COMPANY SPECIAL".No one in the family seems to know anything about it. Who was Bonnie & Company, and what are these decanters used for? (The mating surfaces of the stopper and bottle are not ground, so it does not supply a tight seal.)Thanks,David

Private label bottlings were once popular business gifts. That's what this sort of thing usually is, though sometimes they're personal, to commemorate an anniversary or a birthday, but it's the same principle.

This sounds like a Bar Decanter to me. I have seen one for Bonnie and Company before. In the 19th century most whiskey was sold by the barrel and bars would fill a decanter from the barrel to serve their customers. Distilleries quickly realized that distributing decanters with their name on it would increase the name recognition of their brands. Thus, bar decanters were made and sold to bars at cost.